Hypertension plus diabetes is the most common combination for people 45 to 64, but those 65 or older are more likely to have hypertension plus heart disease. Hypertension plus cancer is the third most common duo for both age groups.

Twenty-one percent of people 45 to 64 have at least two chronic conditions. By age 65, the percentage jumps to 45.

Other conditions tallied in the study are chronic bronchitis, emphysema, asthma, kidney disease and the results of stroke. The study's cancer tally does not include nonmelanoma skin cancer.

"The good news is we're more health-aware, so we're going to doctors and getting diagnosed," said Virginia Freid, health statistician for the CDC and co-author of the study. "And more people are surviving heart disease and cancer, so they're more often on our lists of diagnoses."

Are we more likely to have these conditions or to have been diagnosed with them? Both, said Freid, even though the study only counts diagnoses that participants have from their doctors.

In addition to showing overall increases in multiple conditions, the study says more people 45 to 64 have no or delayed medical care (23.4 percent). And 21.5 percent fail to get the drugs they need. "It's a combination of things — having less insurance, having no insurance or being in denial of your condition," said Freid.

After age 65, though, most people have medical care and the drugs they need. "Having Medicare at this age and acknowledging their conditions" are two main reasons, said Freid.

The biggest culprit behind the statistics, said Freid, is obesity. "It increases your chances of having many of these conditions," she said. "We live in an environment with too much food, the wrong food and too-large restaurant portions."

The study shows few differences between men and women for the younger group. For the older group, though, men are more likely to have multiple chronic conditions.

Racial differences are more distinct. In the younger age group, having multiple chronic conditions is more prevalent among whites and Hispanics than among blacks. In the older group, it is more so among Hispanics. There were not enough Asians in the study to assess their rates, said Freid.

For the younger age group, the higher people's income, the healthier they are. For the older group, income makes less of a difference. "Even if you have the higher income and are working out and eating better, your age still catches up to you," said Freid.

The take-home message, said Freid, is our medical treatment is becoming more complicated. "We're going to more specialists, but our doctors have to look at our health as a whole," she said. "You go to the doctor because you break your leg, for example, but you also have diabetes and high blood pressure.

"If you're older than 65, the doctor should consider the multiple drugs you're taking too. Forty percent of people in this older group are taking at least five drugs. They have interactions and cost a lot of money. All this affects your treatment."

The study was drawn from a sample of 29,523 people. It compares data from 2009 and 2010 to data from 1999 and 2000.